text: A star supplies its own energy from nuclear sources, and hence the temperature equilibrium cannot be defined in terms of incident energy only.
  Cox and Giuli (1968/1984) define radiative equilibrium for a star, taken as a whole and not confining attention only to its atmosphere, when the rate of transfer as heat of energy from nuclear reactions plus viscosity to the microscopic motions of the material particles of the star is just balanced by the transfer of energy by electromagnetic radiation from the star to space. Note that this radiative equilibrium is slightly different from the previous usage. They note that a star that is radiating energy to space cannot be in a steady state of temperature distribution unless there is a supply of energy, in this case, energy from nuclear reactions within the star, to support the radiation to space. Likewise the condition that is used for the above definition of pointwise radiative equilibrium cannot hold throughout a star that is radiating: internally, the star is in a steady state of temperature distribution, not internal thermodynamic equilibrium. Cox and Giulis definition allows them to say at the same time that a star is in a steady state of temperature distribution and is in radiative equilibrium'; they are assuming that all the radiative energy to space comes from within the star.